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C D Claussen

Publications and source records attributed to C D Claussen.

At least 91 records · Page 5Linked to original sources
PubMed2003

Estimation of radiation exposure in 16-detector row computed tomography of the heart with retrospective ECG-gating.

PURPOSE: We sought to evaluate the radiation exposure of cardiac CT scans with 16-row multidetector computed tomography (MDCT). Additionally the possibility of dose reduction by using a ECG-controlled tube current modulation technique was evaluated. METHODS AND MATERIAL: An Alderson Rando phantom equipped with thermoluminescent dosimeters was used for dose measurements. Effective dose was calculated according to ICRP 60. Exposure was performed on a 16-row MDCT scanner with standard protocols for CT coronary calcium scoring (120 kV, 133 mAs, 12 x 1.5 mm) and CT coronary angiography (120 kV, 400 mAs, 12 x 0.75 mm). Exposure was repeated at a simulated heart rate of 60 bpm with ECG-pulsed tube current modulation. RESULTS: Effective dose was 2.9 mSv (male) and 3.6 mSv (female) for the calcium scoring protocol. CT coronary angiography resulted in an effective dose of 8.1 mSv (male) and 10.9 mSv (female). Using ECG-pulsed tube current modulation radiation exposure can significant reduced: by 46 % (1.6 mSv) in calcium scoring and by 47 % (4.3 mSv) in CT coronary angiography. CONCLUSION: MDCT of the heart shows a significant radiation exposure, which can significantly be reduced by ECG-pulsed tube current modulation. Radiation exposure of cardiac MDCT is comparable to CT-examinations of chest or abdomen, but seem to be slightly higher compared to conventional coronary angiography.

Calcinosis↗
PubMed2003

[Multislice TrueFISP-MR imaging for identifying stress-induced myocardial functional disturbances in coronary heart disease].

PURPOSE: This study assesses the left ventricular function using a new multislice cine sequence and determines the diagnostic accuracy of stress-induced wall motion abnormalities in patients with coronary artery disease (CAD). MATERIALS AND METHODS: 15 patients (mean age 57.7 years) with angiographically proven CAD were examined on a 1.5 T whole body system (Magnetom Sonata, Siemens, Erlangen) at rest and during dipyridamole-induced (0.56 mg/kg body weight) stress. Left ventricular function was determined using a multislice (steady-state) sequence (TR 2.3 ms, TE 1.15 ms, slice thickness 10 mm, temporal resolution 77 ms) as well as a standard single-slice true FISP 2D sequence (TR 3.2 ms, TE 1.6 ms, slice thickness 5 mm, temporal resolution 45 ms) as reference. RESULTS: Both cine sequences provide high sensitivity and excellent correlation (r = 0.95) with angiographic findings for the detection of regional wall motion abnormalities. However, the measurement of functional parameters yielded significant differences. End-systolic left ventricular volumes (ESV) were systematically overestimated in the multislice images (mean 78 ml, + 5.8 %) compared with the reference single-slice images (mean 74 ml) (p < 0.05). This resulted in underestimation of the ejection fraction with multislice images (mean 40 %, - 11.3 %) compared with single-slice images (mean 46 %) (p < 0.05). CONCLUSION: The multislice sequence results in a substantial reduction of imaging time and breath-hold periods necessary to cover the left ventricle for functional assessment. The multislice sequence yields adequate images, especially for qualitative determination of wall motion abnormalities. Due to the reduced spatial and temporal resolution of the multi-slice sequence, however, some uncertainty concerning the functional parameters has to be taken into account.

Adult↗
PubMed2003

[Left ventricular functional parameters using ECG-gated multidetector spiral CT in comparison with invasive ventriculography].

PURPOSE: To evaluate the accuracy of left ventricular function using a multidetector CT (MDCT) with retrospective ECG-gating and to compare the results with conventional ventriculography. MATERIALS AND METHODS: In 26 patients, retrospectively ECG-gated MDCT of the heart (Volume Zoom, Siemens, Germany) as well as conventional coronary angiography including ventriculography was performed to exclude or follow coronary artery disease. CT examination (120 KV, 400 mAs) was carried out with 4 x 1 mm collimation (500 ms gantry rotation time). For CT angiography, 150 ml of contrast media was injected intravenously at a flow rate of 4 ml/s. All data sets of the functional cardiac parameters were reconstructed in end-systolic and end-diastolic phase. End-systolic volume (ESV), end-diastolic volume (EDV) and ejection fraction (EF) were determined from multiplanar reformations orthogonally through the cardiac short axis and analyzed using special evaluation software (ARGUS, Siemens). The results were compared with ESV, EDV and EF obtained from invasive ventriculography. RESULTS: In all cases, a sufficient quality of the MDCT images was achieved. EDV (150.1 +/- 16.2 ml MDCT vs. 138.7 +/- 16.9 ml ventriculography; mean difference 11.4 +/- 12.7 ml; r = 0.51) had an acceptable correlation to conventional ventriculography, and ESV (58.1 +/- 14.6 ml vs. 50.2 +/- 13.4 ml; mean difference 7.9 +/- 8.8 ml; r = 0.81) and EF (60.9 +/- 13.6 % vs. 64.9 +/- 12.7 %; mean difference 4.0 +/- 6.2 %; r = 0.79) showed a good correlation. In comparison with invasive ventriculography, MDCT tended to overestimate significantly EDV (p = 0.008) and ESV (p = 0.003) and to underestimate EF (p = 0.001). CONCLUSION: MDCT of the heart with retrospective ECG-gating enables efficient estimation of left ventricular function, providing important additional information of non-invasive cardiac imaging using MDCT. However, EDV and EVS were significantly overestimated and EF was underestimated in MDCT compared to ventriculography.

Aged↗
PubMed2003

[Systematics of imaging artifacts in MRT caused by metallic vascular implants (stents)].

PURPOSE: Imaging artifacts in magnetic resonance tomography (MRT) caused by metallic vascular implants (stents) were characterized systematically in dependence on the material and the construction of the implants as well as with respect to different measurement protocols and for different static field strength B (0). METHODS: Twelve stents, different in material (stainless steel, nitinol, Co-alloy) and/or construction, were examined at B (0) = 0.2 T and 1.0 T with two 2D gradient echo (GE) sequences (TE = 4 and 10 ms), one 3D GE sequence and one spin echo (SE) sequence. The stents were put into water with Gd-DTPA contrast agent. The dependence on the orientation was analyzed for the 9 possibilities of an orthogonal alignment of the stent axis, the direction of B (0), the slice, the read out, and the phase encoding direction. Special interest was given to the visibility of the stent lumen at forced rf excitation, as well as to the influence of broken struts on the signal obtained. RESULTS: For the examined stents GE technique showed, due to spin dephasing regions a total signal loss ranging up to 8 mm away from the stent mashes. The value depends on the stent material, the stent orientation in the scanner and grows with voxel size, echo time and B (0). In SE technique dephasing artifacts vanish and wrong spatial encoding gets visible, rf shielding is more pronounced. The visibility of the stent lumen ranges from nearly unperturbed down to a complete signal loss. An improvement is possible using enlarged flip angles. Broken struts can not be imaged significantly. DISCUSSION: The MR representation of metallic stents commercially available at the time, especially of nitionol stents, can be optimized with a suitable adaptation of the imaging parameters. However, a profound improvement can only be expected from new stent material and design.

Alloys↗
PubMed2002

Improved detection of splenosis in patients with haematological disorders: the role of combined transmission-emission tomography.

The purpose of this study was to evaluate the use of combined transmission and emission tomography (TET) for correct localisation of heterotopic splenic tissue and differentiation of splenosis from other masses. The TET technique comprises the fusion of SPET and CT data obtained using the same imaging device to allow perfect overlap of anatomical and functional images. TET was performed in seven patients who either had haematological disorders and relapsing anaemia or thrombocytopenia after splenectomy or were under immunosuppression for different reasons. These patients presented 20 equivocal lesions on CT or MRI. Presence of splenic tissue was investigated using technetium-99m labelled colloids or heat-damaged red blood cells. Findings of spleen scintigraphy, TET and CT or MRI were compared with respect to localisation of splenosis and correct classification of lesions by CT or MRI. Histological validation was achieved by surgery or biopsy in all cases. All 20 lesions demonstrated by CT or MRI were correctly classified by TET as splenosis. Three additional lesions initially overlooked by CT or MRI could be detected. Diagnostic relevance was highest for intrahepatic, intrapulmonary or pleural splenic implants. It is concluded that TET allows exact localisation of heterotopic splenic tissue in patients with suspected splenosis.

Adult↗
PubMed2002

Alterations in diffusion and perfusion in the pathogenesis of peritumoral brain edema in meningiomas.

Magnetic resonance perfusion and diffusion studies were undertaken to clarify the significance of ischemia in the pathogenesis of peritumoral brain edema in patients with meningiomas. Included in this study were 26 patients with 27 meningiomas and 5 gliomas. Perfusion-weighted imaging (PWI) was performed using a gradient-echo, echo-planar-imaging (EPI) sequence for calculation of the relative regional cerebral blood volume (rrCBV) and the relative regional cerebral blood flow index (rrCBFi). Furthermore, multi-slice spin-echo EPI sequences were applied in order to obtain anisotropic and isotropic diffusion-weighted imaging (DWI). Apparent diffusion coefficient (ADC) values were then calculated for peritumoral brain parenchyma from tumors, with and without edema, using various diffusion sensitivities. Meningiomas without edema demonstrated a minimal increase of perfusion parameters in the peritumoral brain tissue. In contrast, cases with brain edema had highly significant ( p<0.0005) lower rrCBV and rrCBFi. The edema index (EI) correlated strongly with the rrCBV. A fitting procedure resulted into the following mathematical relation: EI=0.1/rrCBV(2). The DWI showed a significantly larger ADC value within areas of brain edema, compared with the normal white matter (0.74 x 10(-3) vs 1.55 x 10(-3) mm(2)/s; p<0.0001). Increases in EI correlated with increases in ADC values. In 31% of the meningiomas associated with edema, areas with increased signal, probable ischemia, demonstrated significantly lower ADC values, in comparison with the rest of the edematous areas. These areas were confined to tissue immediately adjacent to the tumor. In general, the decrease in rrCBV in brain edema represents a consequence from, rather than a cause of, vasogenic edema. Ischemic alterations can be regarded as secondary, facultative phenomena in the pathogenesis of meningioma-related brain edema.

Adult↗
PubMed2002

Early prediction of treatment response to high-dose salvage chemotherapy in patients with relapsed germ cell cancer using [(18)F]FDG PET.

To assess the ability of [(18)F]fluorodeoxyglucose positron emission tomography for the early prediction of response in patients with relapsed metastatic germ cell tumours undergoing salvage high-dose chemotherapy. The role of positron emission tomography was compared with established means of tumour response assessment such as CT scans/MRI and serum tumour marker changes. In addition, positron emission tomography was compared with a current prognostic score which differentiates three prognostic groups with failure-free survival rates ranging from 5-50%. [(18)F]fluorodeoxyglucose uptake of metastases from germ cell tumours as well as CT scans and serum tumour marker were acquired after 2-3 cycles of induction chemotherapy but before the start of high-dose chemotherapy and CT scans/serum tumour marker were compared with the baseline examinations in 23 patients with relapsed germ cell tumours. To evaluate the validity of early response prediction by positron emission tomography, radiological monitoring and serum tumour marker decline, histopathologic response after resection of residual masses and/or the clinical course over 6 months after the end of treatment (relapse vs freedom of progression) were used. Overall, 10 patients (43%) achieved a marker-negative partial remission, three (13%) a marker-positive partial remission, five (22%) a disease stabilization and five (22%) progressed during treatment. Nine patients (39%) remained progression-free over 6 months following treatment, whereas 14 (61%) progressed. The outcome of high-dose chemotherapy was correctly predicted by positron emission tomography/CT scan/serum tumour marker in 91/59/48%. Eight patients with a favourably predicted outcome by CT scans plus serum tumour marker but a positive positron emission tomography prior to high-dose chemotherapy, failed treatment. This results in the following sensitivities/specificities for the prediction of failure of high-dose chemotherapy: positron emission tomography 100/78%; radiological monitoring 43/78%; serum tumour marker 15/100%. The positive and negative predictive values of positron emission tomography were 88 and 100%, respectively. As compared with the prognostic score, positron emission tomography was correctly positive in all patients of the three risk groups who failed treatment. In addition, a negative positron emission tomography correctly predicted a favourable outcome in the good and intermediate group. [(18)F]fluorodeoxyglucose positron emission tomography imaging can be used to assess response to chemotherapy in patients with relapsed germ cell tumours early in the course of treatment and may help to identify patients most likely to achieve a favourable response to subsequent high-dose chemotherapy. In patients with response to induction chemotherapy according to CT scans or serum tumour marker evaluation, positron emission tomography seems to add information to detect patients with an overall unfavourable outcome. It may also be a valuable addition to the prognostic model particularly in the good and intermediate group for further selection of patients who will profit from high-dose chemotherapy.

Adult↗
PubMed2002

Separation of intra- and extramyocellular lipid signals in proton MR spectra by determination of their magnetic field distribution.

In skeletal musculature intramyocellular (IMCL) and extramyocellular lipids (EMCL) are stored in compartments of different geometry and experience different magnetic field strengths due to geometrical susceptibility effects. The effect is strong enough to---at least partly---separate IMCL and EMCL contributions in (1)H MR spectroscopy, despite IMCL and EMCL consisting of the same substances. The assessment of intramyocellular lipid stores in skeletal musculature by (1)H MR spectroscopy plays an important role for studying physiological and pathological aspects of lipid metabolism. Therefore, a method using mathematical tools of Fourier analysis is developed to obtain the magnetic field distribution (MFD) from the measured spectra by deconvolution. A reference lipid spectrum is required which was recorded in tibial yellow bone marrow. It is shown that the separation of IMCL contributions can be performed more precisely---compared to other methods---based on the MFD. Examples of deconvolution in model systems elucidate the principle. Applications of the proposed approach on in vivo examinations in m. soleus and m. tibialis anterior are presented. Fitting the IMCL part of the MFD by a Gaussian lineshape with a linewidth kept fixed with respect to the linewidth of creatine and with the assumption of a smooth but not necessarily symmetrical shape for the EMCL part, the only free fit parameter, the amplitude of the IMCL part, is definite and subtraction leads to the EMCL part in the MFD. This procedure is especially justified for the soleus muscle showing a severely asymmetrical distribution which might lead to a marked overestimation of IMCL using common line fitting procedures.

Extracellular Space↗
PubMed2002

[CT-colonography: current status and future directions in consideration of the technical evolution].

Computertomography and with it CT-colonography evolves technically and also possibilities of data processing proceed rapidly. The current status of CTC can be summarized as follows:The method represents a true alternative to barium enema if technical conditions are given.CTC can be performed with excellent results immediately following an incomplete colonoscopy. In pretherapeutic diagnosis of colorectal carcinoma, CTC can be combined with a staging CT of the abdomen. The recent technical advances with new 16 row technology in image quality and data acquisition - mainly concerning the spatial and temporal resolution - are very promising. Developments in postprocessing of CT data can also contribute to a higher efficiency of labor. Alternative preparation schemata can lead to a more comfortable bowel cleansing and stool labeling can even avoid this procedure, resulting both in an even improved compliance. Radiation exposure in low dose technique is comparable to a double contrast barium enema and can be still reduced by optimisation of scanning parameters.The aim of the following article is (1 to give an overview of the current status of patient preparation, image acquisition and data processing; (2) to review recent clinical trials and experimental studies and to show future directions of CTC with regard to the clinical development.

Colonic Polyps↗
PubMed2002

Non-invasive coronary angiography with high resolution multidetector-row computed tomography. Results in 102 patients.

AIMS: A new generation of multidetector-row CT (MDCT) scanners allows complete coronary coverage using retrospective ECG gating and 1mm slices. The purpose of this study was to investigate the potential of high resolution MDCT angiography with retrospective gating for detection of coronary artery stenoses. METHODS AND RESULTS: A total of 102 patients underwent both conventional and MDCT coronary angiography. After intravenous injection of a non-ionic contrast medium the entire heart was scanned within a single breath hold using 1mm slices. All MDCT data sets were reconstructed with retrospective gating at 20% to 80% in increments of 10% relative to the cardiac cycle. Two blinded independent reviewers analysed image quality for segments 1-4 (right coronary artery), 5-8 (left main, left anterior descending), and 11, 12 (left circumflex). These segments were evaluated for the presence or absence of significant (>or=50%) stenoses. The results were compared with those of invasive coronary angiography in a blinded fashion. Overall sensitivity for the detection of significant stenoses (>or=50%) were 0.86 (reader 1) and 0.93 (reader 2), specificity 0.96 (reader 1) and 0.97 (reader 2), negative predictive value 0.98 (reader 1) and 0.99 (reader 2). CONCLUSIONS: High resolution MDCT angiography with retrospective gating permits the non-invasive detection of coronary artery stenoses with high accuracy if image quality is optimized for each of the three major coronary arteries.

Coronary Angiography↗
PubMed2002

[Endovascular implantation of stent-grafts in the thoracic aorta -mid-term results of a prospective controlled study].

PURPOSE: To evaluate the effectiveness and safety of endovascular treatment of various descending thoracic aortic pathologies with covered stent-grafts as an alternative to open surgery. METHODS: Among 16 patients (5 type B dissections, 5 contained ruptures, 3 aneurysms of the descending aorta, 1 thoraco-abdominal aneurysm, 1 mural thrombosis, 1 patch aneurysm) treated between November 1997 and November 2000, eight patients received Talent stent-grafts and another 8 patients underwent a Gore-TAG stent-graft implantation. A clinical follow-up and control CT scans were obtained after the procedure and then at six-month intervals. RESULTS: Deployment of the stent-grafts was technically successful in all cases. Sufficient aortic reconstruction was achieved in all but one patient who needed surgical treatment. One patient died two days after the procedure from aortic rupture due to retrograde type A dissection. Another patient died 19 months after the procedure from an unknown cause. There was no occurrence of distal embolization, paralysis or infection. During follow-up, all patients remained free from recurrence or late complications of their disease. CONCLUSION: Endoluminal treatment of thoracic aortic pathologies with covered stent-grafts appears to be a safe and feasible method with at least mid-term efficacy.

Adult↗
PubMed2002

[Visualization of coronary arteries in CT as assessed by a new 16 slice technology and reduced gantry rotation time: first experiences].

PURPOSE: First evaluation of image quality of a new 16-slice multidetector-row computed tomography (MDCT) for the assessment of coronary artery disease and lesion detection of the coronary arteries. MATERIALS AND METHODS: On a newly developed 16-slice CT scanner (SOMATOM Sensation 16, Siemens, Forchheim, Germany) a calcium score as well as a contrast-enhanced CT angiography (CTA) were performed on 4 patients with retrospective ECG-gating and a gantry rotation time of 420 ms to exclude or follow-up coronary heart disease. CTA was performed after injecting 120 ml contrast media intravenously. After medication with a ss-Blocker, the heart rate was between 55 and 67 bpm. RESULTS: The scan time for calcium score was 12 s, for CTA 18 s (scan range 15 and 12 cm, respectively). Volume score was between 0 and 256.4. In the CT angiography the entire coronary tree could be visualized in all patients up to the very distal subsegmental branches. In two patients a complete occlusion of the RCA and the LAD were depicted, respectively. In one of these patients, a large aneurysm of the left anterior ventricular wall was also delineated. CONCLUSION: Considering our first experiences with the new 16-slice technology, an excellent visualization of the entire coronary tree including the very distal and side branches due to substantially increased spatial resolution seems to be achievable. In these patients the acquired image quality raises the hope for improved, non-invasive cardiac diagnostics. In larger studies, the clinical impact of this new technology needs to be further investigated.

Aged↗
PubMed2002

[Imaging diagnosis of solitary pulmonary nodules on an open low-field MRI system--comparison of two MR sequences with spiral CT].

OBJECTIVE: To evaluate and compare two fast gradient-echo sequences (GRE) concerning the visualization of solitary pulmonary nodules with an open low-field MRI system in comparison to computed tomography. MATERIALS AND METHODS: Fourteen patients with solitary pulmonary nodules detected by spiral CT ranging in size from 6 mm to 42 mm (mean 20 mm) underwent MRI on an open 0.2 T scanner using a spoiled 2D GRE (2D FLASH; TR/ TE/Flip = 100 ms/7.5 ms/30 degrees ) and a totally refocused 2D steady-state GRE (True-FISP; TR/TE/FA = 7.3 ms/3.5 ms/80 degrees ). The image quality concerning artifacts (by flow, breathing and susceptibility) and the morphologic characteristics of the nodules were scored and compared with CT by two independent radiologists. The diameters of the nodules measured by MRI were compared with CT measurements. The sequences were also evaluated with regard to the signal-to-noise ratio (SNR) of the lesion. RESULTS: All lesions were detected with the 2D FLASH sequence. True-FISP failed to find a granuloma with a size of 6 mm. The 2D FLASH was rated significantly superior to true FISP concerning image quality artifacts by susceptibility as well as concerning to CT the presentation of nodule characteristics. In MR images, the size of lesions was significantly smaller than in CT images for both sequences: for 2D FLASH the mean difference was 0.9 mm and for true FISP 2.6 mm. The SNR of the nodules was significantly higher for the 2D FLASH than for the true FISP. CONCLUSION: In low field MRI, the 2D FLASH sequence is superior to the 2D true FISP sequence in imaging of pulmonary nodules. With the 2D FLASH sequence nodules of 6 mm or larger in size can be visualized.

Aged↗
PubMed2002

[Characterization of motion artifacts in multi-slice spiral CT].

PURPOSE: Motion artifacts in multi-slice spiral CT (MSCT) resulting from object motion in and against the table feed direction (z-direction) are examined using a spherical phantom. For image interpretation of complex anatomic structures, qualitative reference points are, also applicable to selected, which are ECG-gated cardiac imaging. In this case the motion of the coronary vessels in phase with the cardiac contraction must be considered. METHODS: Measurements are obtained with a multi-slice spiral CT with a rotation time of 500 ms for 4 x 1.0 mm and 2 x 0.5 mm collimation. The phantom consists of an acrylic glass body with imbedded glass beads of 1, 2, and 3 mm diameter. The object motion is sinusoidal with an amplitude of 5 mm and frequencies of 60/min and 90/min. Compensation of the table feed by object motion is examined as a special case. RESULTS: Small parameter changes can induce a strikingly different image quality, and the moving objects emerge in different slices. Depending on the phase of the movement with respect to the CT scan, objects up to a size of 3 mm can vanish completely or appear hyperintense in the image. The model investigated is also applicable to ECG-gated cardiac imaging for the detection of stenosis. It can explain variations in the reproducibility and absolute score values of the calcium scoring. CONCLUSION: The presented considerations and results must be taken into account in image interpretation with possible object motion in the z-direction. Variations in the determination of the degree of stenosis or in calcium score measurements can be explained by different vessel motion during the diastolic heart phase.

Artifacts↗
PubMed2002

[MRI of intraosseous fistulous systems and sequesters in chronic osteomyelitis with standard spin echo sequences, highly selective chemical-shift imaging, diffusion weighted imaging, and magnetization-transfer].

PURPOSE: To study and test the impact of modern MRI techniques in diagnostic imaging in the evaluation of intra-osseous fistulous systems and sequesters. MATERIALS AND METHODS: In a prospective study, nine patients with chronic osteomyelitis of the legs were examined by MRI. Patients with clinical signs of osteomyelitis requiring surgery were included in the study. T1-weighted spin echo (SE) sequences, proton density (PD) and T2-weighted fast spin echo (FSE) sequences, water- and fat-selective FSE sequences, and diffusion weighted (DW) PSIF sequences were used preoperatively. Furthermore, magnetizing transfer (MT) with gradient echo (GRE) sequences was evaluated. RESULTS: Water selective sequences revealed the highest sensitivity for the detection of fistulas (100%), providing the best delineation of the extent of the entire fistulous systems. Fat-selective sequences (sensitivity 55.6%) and T1-weighted sequences (sensitivity 77.8%) displayed fistulas as hypointense bands, which, however, cannot be well differentiated from cortical bone in the transcortical areas. PD and T2-weighted images were found to have a poor sensitivity (55.6% and 66.7%) for fistulas in any location. The sensitivity of water-selective sequences to demonstrate intraosseous sequesters was 100%. The sensitivity was low for the other sequences. In 4 of 5 patients with surgically proven infection, DW and MT revealed an abnormal spatial distribution, with high diffusion in the central parts of the fistulas and high MT effect peripherally surrounding a weak MT effect centrally. CONCLUSION: Water-selective sequences are superior when demonstrating fistulous systems and intraosseous sequesters. The combined use of MT and DW sequences seems to allow a differentiation between solid granulation tissue and liquid pus.

Adult↗